Plural communication modes exist in mobile communications represented by a mobile-phone. For example in Europe, in addition to GSM which has been in widespread use as the second generation wireless communication system, and EDGE which has enhanced a data transmission speed of GSM, there is W-CDMA of which the service has started in recent years as the third generation wireless communication system. In North America, in addition to DCS and PCS which are the second generation wireless communication systems, cdma1× has been in widespread use as the third generation wireless communication system. GSM stands for Global System for Mobile Communications, EDGE stands for Enhanced Data rate for GSM Evolution, W-CDMA stands for Wide-band Code Division Multiple Access, DCS stands for Digital Cellar System, PCS stands for Personal Communication System, and cdma1× stands for Code Division Multiple Access 1×.
Non Patent Literature 1 in the following describes that matching technique by a transmission line transformer (TLT) is employed for multi-octave impedance conversion at an RF frequency and a low-end microwave. Traditionally, in a power amplifier, in order to realize a transformer which converts a super low impedance into 50Ω in a band of an octave or beyond, a lot of inductors, capacitors, transmission lines, or combination of them are generally used in a ladder circuit. The traditional technique which uses these component parts results in a restricted frequency band and a large circuit size. A transmission line transformer (TLT) which uses a section of straight lines or coils of the transmission lines, coupled with each other, results in a wide band and a small circuit size. Non Patent Literature 1 in the following also describes that the present type of transformer can be designed to employ multilayer wiring manufacturing technology of, for example, a wiring circuit substrate, a low temperature co-fired ceramics (LTCC), a high temperature co-fired ceramics (HTCC), a monolithic silicon (Si), or a gallium arsenide (GaAs) IC.
Non Patent Literature 2 in the following introduces a Guanella-type and a Ruthroff-type transmission line transformer (TLT), and describes that an unbalanced Guanella type transmission line transformer (TLT) is formed by using a three-layer wiring over a GaAs substrate.
Non Patent Literature 3 in the following describes that a transmission line transformer (TLT) is different in that energy is transferred to an output circuit by a transmission line mode, in contrast with the traditional transformer in which energy is transferred by magnetic flux coupling. Since stray inductance and parasitic capacitance are generally absorbed by characteristic impedance of a transmission line, the transmission line transformer (TLT) is supposed to exhibit a broader bandwidth and a higher efficiency than the traditional transformer as a result. An off-chip transmission line transformer (TLT) is used for conversion of a single-ended signal to a differential signal and its inverse conversion in a low noise amplifier (LNA) for 2.4 GHz Bluetooth application.
Non Patent Literature 4 in the following describes that a transformer is a useful component for impedance matching, however, consideration must be taken into internal wiring capacitance in a frequency band of 2-30 MHz, and that a Guanella-type and a Ruthroff-type transmission line transformer (TLT) are, on the contrary, useful at a tremendously high electric power level, and are simply configured, inexpensive, light-weighted, and can treat a broad bandwidth. In a wide-band high-output RF linear amplifier of a frequency band of 2-30 MHz used for SSB and AM communication, a transmission line transformer (TLT) wound around a ferrite toroid is used for a matching circuit of an interstage and an output of a multistage amplifier.
Non Patent Literature 5 in the following describes the use of a choke coil inductance as a load of a power amplifier for RF communications for which a high efficiency is required. Non Patent Literature 5 in the following also describes that the choke coil inductance suppresses higher harmonics of current supplied from a DC power supply to an amplifier.
[Non Patent Literature 1] Inder J. Bahl; “Broadband and Compact Impedance Transformers for Microwave Circuits”, IEEE MICROWAVE magazine, PP. 56-62, August 2006.
[Non Patent Literature 2] J. Horn et al; “Integrated Transmission Line Transformer”, 2004 IEEE MTT-S Digest, PP. 201-204.
[Non Patent Literature 3] Bill Toole et al; “A Low Voltage, Low Power RF CMOS LNA for Bluetooth Applications using Transmission Line Transformers”, Proceedings of the 27th European Solid-State Circuits Conference, 2001, ESSCIRC, 18-20 Sep., 2001, PP. 433-436.
[Non Patent Literature 4] OCTAVIUS PITZALIS et al; “Broadband 60-W HF Linear Amplifier”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-6, NO. 3, JUNE 1971, PP. 93-103.
[Non Patent Literature 5] Brett E. Klehn et al; “AN EXACT ANALYSIS OF CLASS-E POWER AMPLIFIERS FOR RF COMMUNICATIONS”, Proceedings of the 2004 International Symposium on Circuits and Systems, PP. 277-280.